Many employers, law enforcement, military and even domestic consumers perform drug screening on a regular basis. Due to cost issues and ease of use, colorimetric methods are commonly used. Test reagents are reacted with suspect samples or urine, and color changes are observed. These methods are also referred to as spot or presumptive tests. Unfortunately, many of these tests are nonspecific, resulting in false positives, or if the wrong test is used, a substance abuser may go undetected. The list of pharmaceuticals and food products known to produce false positives on colorimetric tests is expansive, and the list will grow as more pharmaceuticals are introduced into the market. For example, methapyriline, the active ingredient found in some over the counter (OTC) medications, produces a false positive for stimulants. Valerian herbal tea, commonly used as a sleep aid, produces false positives for barbiturates. Employees that are subjected to urine testing are often instructed not to ingest certain OTC drugs or specific foods prior to testing. Some common tests require skilled interpretation since the results are concentration-dependent for both the reagent and sample. Thus, these so-called presumptive tests yield questionable results and require either additional colorimetric or expensive confirmatory tests.
A traditional forensic science method for identifying illegal substances entails the use of sequential spot tests to identify specific drugs. An example of a process using sequential testing is found in U.S. Pat. No. 4,104,027 for the presumptive identification of narcotics and drugs of abuse. The procedures for identifying a suspected drug entails following a series of sequential tests determined by the results of the preceding test. Examples of sequential testing procedures are found throughout the scientific literature and numerous websites.
Numerous types of drug test kits are on the market, including disposable test strips that are impregnated with specific test chemicals. Test kits that utilize disposable strips often have multiple test sites on the same strip, and each site is used to identify a specific drug class (e.g. stimulant, hallucinogen, depressant, or narcotic). Thus, a specific color change on one site may be used to identify the presence of a stimulant. The color change on a different site may be used to identify the presence of a narcotic. The technology for embedding chemicals on disposable test strips is well established for detecting the presence of illegal drugs.